1. Technical Field
The present invention generally relates to force sensors and more particularly, force sensors capable of measuring extremely small forces.
2. Discussion
As is generally known in the art of force testing, sensors are utilized for measuring forces in horizontal and vertical directions. Generally, these sensors are first calibrated over an expected range prior to there use in measuring unknown forces. To accomplish this, conventional test instruments employ load cells or strain gauges for measuring a force directed on a flexible member. The strain gauges and load cells transform sensed mechanical force into an electrical signal. From the electrical signal, a stress-strain curve of the flexible member can be calibrated and the flexible member can be used in conjunction with the sensor in a stand alone capacity to measure forces directed across the flexible member.
To calibrate a flexible member using strain gauges, the strain gauges are usually coupled on opposite sides of the flexible member. The flexible member is then deflected by a displacement generator over a preset range. The stress-strain curve of the flexible member is calculated from the preset displacement and the measured load which is derived from the electrical signals generated by the strain gauges.
Similarly, flexible members can be calibrated through use of load cells and other force transducers. The flexible member is operably coupled to the load cell such that a load is applied thereto when the flexible member is displaced. The load and displacement are then used to calculate a stress-strain constant. Again, the flexible member and load cell can then be removed from the test apparatus and used to measure unknown forces.
However, conventional sensors, such as strain gauges and load cells, are not sensitive enough to measure very small forces, e.g., less than 0.1 grams, directed across the flexible member. Thus, the sensor and flexible member can not be used to measure minute forces, such as water drag on sea-going vessels or in flow tanks, air pressure from ducts and over surfaces and frictional forces in bearings. Furthermore, known calibration techniques are limited by stiction between components which is difficult to measure, eliminate, or account for when measuring minute forces. Also, many calibration techniques are restricted to utilizing forces directed in only a limited range due to system torque.
Therefore, it is desirable to provide an apparatus enabling simple and accurate calibrating of a flexible member. It is further desirable to provide an apparatus capable of calibrating a flexible member capable of measuring forces less than one tenth of a gram. Furthermore, it is desirable to provide an apparatus capable of redirecting forces to the direction of the force being measured.